Defects in blastocyst implantation can prevent pregnancy or set the stage for clinical complications of pregnancy that present at advanced gestational ages. A critical variable of the implantation equation is uterine receptivity, which determines whether a blastocyst can attach to and invade the endometrium. However, the cellular and molecular mechanisms underlying uterine receptivity are not well understood. Our lab has identified adrenomedullin (Adm, AM) as a maternal- and fetal-derived endocrine factor that is important for the establishment and maintenance of a healthy pregnancy. Using genetic mouse models, we have uncovered a subfertility phenotype in Adm+/- females, which birth smaller litters that are abnormally spaced and overcrowded in utero. Importantly, we have shown that the maternal genotype is causative of this phenotype, underscoring the importance of maternal-derived AM dosage in the uterus during implantation. However, further investigation has been limited by the embryonic lethality of Adm-/- pups, so the subfertility phenotype of Adm+/- females remains unexplained. Signal transducer and activator of transcription 3 (STAT3) is a candidate regulator of Adm expression that has been shown to abolish uterine receptivity and fertility by interfering with junctional remodeling in the uterine luminal epithelim. My preliminary in vitro and in vivo studies suggest that AM contributes to proper tight junction formation in the uterus. Therefore, I propose to test the hypothesis that the STAT3-Adm axis contributes to fertility by providing organizational cues to junctional proteins in the uterus durig the peri- implantation period. Aim 1 will define the relationship between STAT3 and Adm in vitro using standard ChIP, luciferase, qRT-PCR, and ELISA assays. In Aim 1, I will also test whether AM directly promotes the formation of pinipodes, markers of uterine receptivity, or the formation of a protective barrier surrounding the newly implanted embryo. Aim 2 will use loss-of-function mouse models to characterize the contributions of AM signaling in different uterine compartments to fertility and the junctional integrity of the uterus during implantation. Specifically, floxed calcitonin receptor-like receptor (Calcrl, CLR) mice will be crossed to Lactoferrin-iCre and Amhr2-Cre lines to delete CLR, the AM receptor, in the uterine epithelial and stromal compartments, respectively. I will then subject Cre+ and Cre- animals to a comprehensive fertility phenotyping analysis. I will also assess whether loss of AM signaling in the epithelium and stroma affects junctional integrity in these compartments during the peri-implantation period. Results from these experiments will provide insight into the control of Adm expression in the uterus and its compartment-specific contributions to fertility, potentially via organization of cell- cell junctions. Ultimately, these studies will advance our understanding of uterine receptivity and inform efforts to develop therapeutics for infertility; preventative strateies for complications of pregnancy; and novel contraception methods.